docs: def handle_unset_evidence(self, line: str, position: int, tokens: ParseResults) -> ParseResults:
          """Unset the evidence, or throws an exception if it is not already set.
  
          The value for ``tokens[EVIDENCE]`` corresponds to which alternate of SupportingText or Evidence was used in
          the BEL script.
  
          :raises: MissingAnnotationKeyWarning
          """
          if self.evidence is None:
              raise MissingAnnotationKeyWarning(self.get_line_number(), line, position, tokens[EVIDENCE])
          self.evidence = None
          return tokens